1. Technical Field of the Invention
The present invention relates to rotary electric machines for vehicles, such as automobiles and trucks.
2. Related Art
Segment type coils wound about or embedded in a stator are known well in the art. Such coils wound about or embedded in a stator (hereinafter referred to as “stator windings”) typically consist of a number of U-shaped electrical conductors. Segment type stator windings are typically made of copper, however, as disclosed in Japanese Unexamined Patent Application Publication No. 11-191946, windings made of aluminum are also known. Aluminum conductors can provide such merits as reducing weight, and preventing corrosion that may be caused by being in contact with water.
When stator windings are constituted of conductors made from copper, electrical connection has been readily established between the stator windings and a rectifier by connecting copper leads of the stator windings to a terminal of the rectifier, which is also typically made of copper, by using TIG (tungsten inert gas) welding or the like. Since both the leads and the terminal are made of the same material, or copper, solder bonding has also been readily performed. Also, the copper-conductor stator windings have provided good serviceability, such as readily available repair in the market.
On the other hand, when stator windings are constituted of conductors made from aluminum, electrical connection between leads of the stator windings and a terminal of a rectifier is difficult to achieve. This is because aluminum structuring the conductors of the stator windings and copper structuring the terminal of the rectifier are dissimilar metals having different melting points, and thus are not suitable for TIG welding or the like.
From the technical point of view, aluminum and copper can be joined, for example, by ultrasonic welding and friction welding, however, such welding techniques require dedicated equipment. This raises a problem in that assembling of parts cannot be readily carried out in overseas manufacturing bases or in small-scale domestic production lines. Further, since soldering is difficult between the copper conductors of the stator windings and the aluminum terminal of the rectifier, another problem is raised in that serviceability, such as repair in the market and replacement of parts, is considerably deteriorated.
In addition, rotary electric machines mounted on an engine are under extreme vibration conditions. In this regard, when the stator windings including the leads are made of aluminum whose mechanical strength is inherently low, the leads which are run relatively longer distance than other conductors of the stator windings present a problematic deterioration in vibration resistance.